The invention relates to a grapple apparatus for grasping, lifting, and releasing loads, particularly adapted for handling loose material such as hay or mulch, and the method of operation of the apparatus.
Grappling devices are common in a number of agricultural and industrial fields and there is a steady demand for improved material-handling apparatus and methods. One fairly recent application for which a well adapted grapple would be useful is the practice of helimulching, i.e. spreading mulch and related materials over large land areas by dropping the material from a helicopter at an altitude suitable to gain the dispersal required. While this is not the only intended application of the present invention, it points out several directions which, individually or in combination, could present goals for improvement over prior art grapples. Specifically, a device used for helimulching must be efficient in its use of people, time, and weight, as many aerial grappling applications take place in wilderness areas where ground-based options are not safe or practical to pursue, and the cost of helicopter time, fuel, and labor is high. An effective grapple for this purpose must also be robust in its ability to manage shock loading, to which helicopters are especially sensitive.
There is no prior art device known to the inventors that combines all of the above strengths. However, an inventory of a few selected prior art grapples will identify the problems traditionally encountered in the development of related machines.
U.S. Pat. No. 52,134, issued Jan. 23, 1866 to Buckman, discloses the semi-automatic operation of a horse hay-fork having fork tines or fingers at the lower ends of its frame halves which are guided, through a combination of levers and hinges, to an essentially horizontal position when retaining a load and an essentially vertical position when releasing a load. The release control requires only the pulling of a rope. However, the rope must be pulled manually, making such a grapple ineffective for working at altitude or in heavily sloped and wooded areas where human access is limited.
U.S. Pat. No. 1,462,787, issued Dec. 19, 1921 to Degendorfer, offers an example of an agricultural fork which explicitly eliminates the need for direct manual intervention with the machine itself; the machine can be controlled remotely by a derrick operator. In this machine the weight of the load even provides some advantage in that it exerts forces on the machine causing it to retain its closed position more firmly. However, the operation still requires multiple cables and therefore some operator skill, and the machine is still confined to ground-based operation.
U.S. Pat. No. 2,815,242, issued Dec. 3, 1957 to Kenyon, discloses a tongs-like device also featuring the intelligent use of weight to help grasp a load, but the weight in this case takes the form of a counterweight, which would dramatically reduce efficiency in a force- and fuel-critical helicopter-towed operation.
Another effective ground-based use of weight is found in U.S. Pat. No. 4,943,099, issued Jul. 24, 1990 to Gabriel, for a magnetic cargo hook that automatically releases when it hits the ground, due to its weight being transferred from a load cable to the ground. However, for aerial operations, the ground-based release would severely limit available altitude and likely applications.
More recently, U.S. Pat. No. 5,653,489, issued Aug. 5, 1997 to present co-inventor Fandrich, provides the best prior art reference as it takes several steps in the right direction while still leaving ample room for improvement. The grapple disclosed in that patent is specifically designed for aerial operation and as such is both lightweight and strong, so that helicopter payload can be maximized. The grapple features shock damping devices to reduce operator risk and fingers capable of squeezing tightly and releasing slowly. However, this earlier grapple is best suited for certain types of materials, particularly for logs, as they are able to be grasped firmly when sufficient clamping force is available. Other materials, especially loose materials such as mulch, do not submit as readily to this type of grabbing action. Minimally, a series of improvements to the existing machine would be required, none of which would be obvious at first.